Let's disassemble the compressor body of these two models to ascertain.
Firstly , It's easy to distinguish the model from the compressor look,
1. A letter " M" ( medium size ) on TM55 body
2. Silver paper label with detailed model code
3. Packing carton with detailed model code
Secondly, Both of these 2 models are same piston diameter 38.5 mm , but a little difference in stroke.
TM55----33.7 mm
TM65----38.9 mm
In the end , their cooling capacity is different.
TM55---550 CC
TM65---635CC